Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 265)

App-6
IM 04L31A01-17E
Appendix 4 Output Flow of FIFO Data
Overview of the FIFO Buffer
The CX has a dedicated internal memory for outputting measured/computed/control
data. The memory structure is FIFO (First-In-First-Out). Measured/computed/control
data is constantly acquired to the internal memory at the specified acquisition interval
(FIFO acquisition interval, set with the FR command). By using this function, it is
possible to read measured/computed/control data that has been saved at specified
intervals regardless of the frequency at which the PC periodically reads the measured/
computed/control data.
The following example shows the case when the acquisition interval is 1 s and the
capacity of the FIFO memory is for 8 intervals.
Most recent acquire
position : WP
Block1
3
4
5
6
7
2
Block8
Previous read
position : RP1
Current read
position : RP2
Acquiring measured/computed/control data
• The measured/computed/control data is acquired to the internal memory at an interval
of 1 s.
• Measured/computed/control data is acquired to positions 1 through 8 in order. After
acquiring to position 8, the next data is acquired to position 1.
Reading the measured/computed/control data (FF GET command is used.
Logging output)
Outputs the data from the previous read position (RP1) to the most recent acquisition
position (WP).
In this example, more than 2 s has elapsed from the previous read operation. Therefore,
data in positions 5 and 6 is output.
Reading the measured/computed/control data (FF GETNEW command is used.
Logging output)
Outputs the data from the most recent acquisition position (WP) back to the specified
number of blocks.
If the number of block is set to 5 in this example, data of blocks 2 to 6 is output.
The size of internal memory allocated for the FIFO buffer (FIFO buffer data length) is
equal to the size for acquiring 60 intervals (60 s total for a scan interval of 1 s).